Embodiments of the present invention relate to a thin film transistor liquid crystal display (TFT-LCD) array substrate and a method of manufacturing the same.
Thin film transistor liquid crystal displays (TFT-LCDs) device have the advantages of small volume, low energy consumption, low radiation and the like, and thus have prevailed in the flat plate display market. As for TFT-LCDs, the performance, yield and cost are mainly determined by an array substrate of a TFT-LCD and a manufacturing method thereof. In order to effectively reduce the cost and improve the yield, the process of manufacturing a TFT-LCD array substrate is gradually simplified from the initial 7-mask process to the present 4-mask process employing a half-tone mask or a gray-tone mask.
Presently, the manufacture of a TFT-LCD array substrate can be performed by forming a series of thin film patterns through a series of patterning process. Generally, one layer of thin film pattern is formed through one patterning process. In the 4-mask process, an active layer, a date line, a source electrode, a drain electrode and a TFT channel region can be formed by one patterning process with a half-tone mask or a gray-tone mask. The active layer comprises a semiconductor film and a doped semiconductor film (ohmic contact film) that are stacked in order. During forming the TFT channel region, the doped semiconductor film is etched by a dry etching process. In order to etch away the doped semiconductor film in the TFT channel region and realize the uniformity and selectivity of such etch, an over-etching process is performed until a portion of the semiconductor film provided below the doped semiconductor film is etched. Thus, the semiconductor film must have a large thickness, such as 1500 Å-3000 Å.
According to the definition of the turn-off current of a thin film transistor, the turn-off current of the thin film transistor is proportional to the thickness of the semiconductor film. The turn-off current of the thin film transistor is increased with the increase of the thickness of the semiconductor film. Because of the increased turn-off current of the thin film transistor, the leakage current is increased, the period, during which the voltage of a pixel electrode is held, is shortened, and thus the performance of the TFT-LCD array substrate comprising the thin film transistor as a switch element for a pixel is degraded. Furthermore, during etching the doped semiconductor film and the semiconductor film through a conventional dry etching process, the surface of the semiconductor film in the TFT channel region is roughed due to the physical bombing, and thus the performance of the TFT-LCD array substrate is further degraded. In addition, during forming the TFT channel region by using the half-tone mask or the gray-tone mask, failures (for example, the short circuit between the source electrode and the drain electrode, the open circuit of the channel region, and the like) are caused by the multiple-step etching process, and thus the yield is severely reduced.